Ata Safdar, head of Reckitt Benckiser Korea and Japan, bowed several times in apology before an audience that included victims and their families, among them a 13-year-old boy who now uses an oxygen tank to breathe.
The news conference in a Seoul hotel marked the first public acceptance of responsibility by the firm for its role in a bitter controversy that has raged since 2011.
The government said last year that 92 people were believed to have died from causes related to the humidifier products - not all them marketed by Oxy Reckitt Benckiser, which was the group's South Korean arm at the time.
"Today's apology, was about acceptance of responsibility for the harm that Oxy HS (humidifier sterilisers) has caused," Safdar said.
Ata Safdar, head of British firm Reckitt Benckiser Korea, bows during a press conference in Seoul, South Korea. Source: AAP
"This is the first time we are accepting the fullest responsibility, and we are offering a complete and full apology.
"We were late, five years have passed, we are also apologising far too late. This is what we are apologising about."
As he spoke, a man stepped on to the stage, shouting expletives and slapping him on the back of the neck.
"This is heartbreaking," Safdar said as he asked to be allowed to continue. "I apologise again. I would request that I am allowed to finish my statement, please."
Another man who mounted the stage shouted: "It's too late."
Sales of the sterilisers, a liquid added to the water of humidifiers, were suspended by the South Korean government in 2011.
Safdar said some 178 users of its products are among those believed by the South Korean government to have been affected, and he outlined a plan to set up a compensation panel.
South Korea says 530 people had registered claims since 2011 of lung ailments from using humidifier sterilisers marketed by Oxy Reckitt Benckiser, and similar products marketed by other firms.
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South Korea is believed to be the only country where the products were sold, according to a government official.
South Korean prosecutors have opened a criminal investigation against makers of the products.
The company changed the name of its local unit to Reckitt Benckiser Korea in 2014.
Reckitt Benckiser's global brands include Dettol antiseptic wash and Durex condoms.
Monday's apology follows a written statement last month by the local unit of the company for failing to communicate more quickly with victims and their families. Last month, the firm established a 5 billion won ($4.4 million) "humanitarian fund", which was in addition to a 5 billion won fund set up in 2014.
($1 = 1136.7000 won)
